The solution may be working out, but WDM drivers are the DirectMusic drivers and the ordinary midi driver is the old fashioned MME driver, hence you can send simultaneous midi messages to the same device.
MME drivers aren’t always time precise though and depending on the soundcard, not all soundcards have WDM drivers so this solution may not be accessible for all people.
But i guess currently this is the best solution there is.
has this feature been implemented yet? i’m happy as long as renoise lets me output sysex to the devices without any 3rd party hacks. i have a couple of synths that require sysex for the more obscure features.